Pet robots (e.g., AIBO (trademark)) have been commercialized for entertainment use and other uses. They can take various actions when users call them or touch them.
A robot of this type has sensors that detect the user's voice, the user's motion, and other stimuli. The robot stores a program that makes it “grow” to be a pet having specific character, in accordance with the stimuli it received in the past. The robot will grow to be friendly with people if the user often plays with it. If the user does not play with the robot so often, the robot will grow to be fond of playing by itself.
It is desired that growth patterns, as many and as complex as possible, be prepared for such an entertainment robot. For example, a robot friendly with people may be programmed to change it attitude to some degree, from person to person who contacts with it. In this case, the robot will be lovelier to its user.